ENGINEERING. 



249 



saving upon present rates of freight and insur- 

 ance between the Gulf States and Atlantic and 

 foreign ports, which would be effected by a 

 Florida ship-canal, would be at least 25 per cent. 

 The drainage area available for the water-sup- 

 ply amounts to 1,200 square miles. The aver- 

 age annual rainfall is 54 inches at St. Mary's, 

 and somewhat greater in the interior. It would 

 afford some 1,200 cubic feet of water per sec- 

 ond available for feeding the canal, sufficient 

 for the supply of the canal if it can be all util- 

 ized. About one fourth of this, the actual sup- 

 ply, or one sixteenth of the total precipitation, 

 must be stored away in reservoirs during the 

 wet season for use in the dry season. The res- 

 ervoir could only be economically constructed 

 by embanking the margins of Okefinokee 

 Swamp, and thus forming two vast shallow 

 ponds, one on each side of the canal. 



New lines for canals have been surveyed in 

 Germany to connect all the principal navigable 

 rivers. The canalization of the Main is pro- 

 posed, between Frankfort and Mayence, a canal 

 connecting the Rhine with the Weser and Elbe, 

 one from Ems to the Jahde, one from the El- 

 ster to the Saale, two others connecting the 

 Spree with the Elbe and with the Oder, one 

 connecting the Oder with the Danube, and 

 canals between Berlin and the cities of Ros- 

 tock and Stettin. Another project is the Bal- 

 tic and North Sea Ship-Canal, planned by Dahl- 

 strom, to go from the Bay of Kiel to Bruns- 

 buttel in the estuary of the Elbe. It is to 

 have a minimum depth of 20f feet, a width at 

 the surface of 160 and at the bottom of 64 feet. 

 A peculiar system of reservoirs and locks has 

 been designed to increase the depth at will to 

 25 or 26 feet, so as to float the heaviest iron- 

 clads in the German navy. It is estimated that 

 this canal can be completed in six years, at a 

 cost of about $18,750,000. 



The constant shifting of the channels of the 

 "Western rivers, owing to the erosion of the light 

 prairie soil of their banks, causes the double 

 evils which have long been felt : that of uncer- 

 tain and insecure navigation, and that of the 

 instability and frequent destruction of riparian 

 property, evils which increase with the growth 

 of population and prosperity in the Mississippi 

 Valley. The rapidity and extent of the dis- 

 placement of river-beds increases in geomet- 

 rical progression with the swiftness of the cur- 

 rent. The erosion of the banks and the deposit 

 of the material washed out causes the deflection 

 of the current, and the gradual formation of 

 great bends. The river returns, after a circuit, 

 sometimes of many miles, to its old bed at a 

 point not far below the spot where it deviated. 

 The narrow neck of land between is eaten away 

 by the impact of the current on the lower bank 

 at the first bend, and bars are formed in the 

 loop until a cut-off is formed; and then the 

 sudden increase of slope disturbs the regimen 

 of the river for many miles above and below ; 

 the banks below are washed away, new hollows 

 excavated and bars deposited, the formation of 



new loops hastened, and the same transforma- 

 tions of the channel and alterations in the ve- 

 locity of the current reproduced farther down. 

 The report of Captain Hanbury, of the Engi- 

 neer Corps of the Army, on the condition of 

 the Missouri River near Omaha, describes sim- 

 ple and inexpensive devices, by the skillful 

 application of which the mutable regimen of 

 these rivers can be controlled, their channels 

 rectified and conserved, the navigable way kept 

 clear, and the farmsteads and urban sites along 

 their banks rendered secure. This is accom- 

 plished by arresting the sediment carried down 

 by the river, and causing the deposits to take 

 place where they will preserve or improve the 

 channel, and either increase or lessen the slope 

 of the bed, according to the requirements. The 

 most effective contrivance for filling up a chan- 

 nel-bed when it is desired to deflect the chan- 

 nel into a new course, is a floating-brush dike, 

 technically known where it is used as the 

 " weed." It is made by nailing or wiring 

 scraggy brush to saplings 20 or 30 feet long, 

 and four to eight inches in diameter. The 

 brush is sometimes made fast to a length 

 of rope instead of to saplings. These weeds 

 are anchored from 10 to 20 feet apart in the 

 stream where the bed is to be filled up. The 

 anchor is of sufficient weight to withstand 

 the force of the current. To the down-stream 

 end is attached a buoy to prevent the weed 

 from being driven to the bottom by the press- 

 ure of the current. The action of these float- 

 ing dikes is to retard the current and grad- 

 ually check it, causing a portion of the solid 

 matter which is rolling along the bottom, or 

 held in suspension, to be arrested and pre- 

 cipitated. The sedimentation caused by these 

 dikes is remarkably rapid, a single season often 

 sufficing to build up the area over which they 

 are stretched to the ordinary high -water 

 level. Another device for the same purpose 

 is the willow curtain. This is made of wil- 

 lows an inch or more in diameter, fastened 

 parallel to each other, six or eight inches 

 apart, with wires. The curtains are anchored 

 athwart the current by rows of weights at- 

 tached to the bottom edge, and are held up 

 against the current, in a perpendicular or in- 

 clined position, by floats fastened to their up- 

 per edge. A screen made entirely of wire has 

 been used in the same way as the willow cur- 

 tain, with very satisfactory results. The wire 

 is woven like a seine, and entangles rootlets 

 and vegetable filaments, which accumulate and 

 form a mat dense enough to check the velocity 

 of the current. These curtains perform the 

 same service as the brush-dikes. The protec- 

 tion of banks exposed to the impact of cur- 

 rents is another important task in this branch 

 of hydraulic engineering. The bank is graded 

 to a slope of two in three, or a less grade. This 

 is inexpensively performed by hydraulic force- 

 pumps. Wattled mats of brush or willow are 

 then spread down the bank from the flood- 

 limit, and along the incline of the river-bed, 



